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A firmware hard reset may be initiated by various mechanisms including a UART interface, TWI sideband interface from BMC, MRPC command from userspace, etc. The switchtec management driver is unaware of these resets. The reset clears PCI state including the BARs and Memory Space Enable bits, so the device no longer responds to the MMIO accesses the driver uses to operate it. MMIO reads to the device will fail with a PCIe error. When the root complex handles that error, it typically fabricates ~0 data to complete the CPU read. Check for this sort of error by reading the device ID from MMIO space. This ID can never be ~0, so if we see that value, it probably means the PCIe Memory Read failed and we should return an error indication to the application using the switchtec driver. Link: https://lore.kernel.org/r/20211014141859.11444-2-kelvin.cao@microchip.com Signed-off-by: Kelvin Cao <kelvin.cao@microchip.com> Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.